[Elecraft] [K2] VCO Not Oscillating

[Joseph Baxley via Elecraft]

Don,

Thanks again.  I had one question from your last email.  Did you mean C60?   I couldn't find C50 in the VFO circuit.  I shorted C60 which put the drain to ground.  Still no help.  The BFO is working though, so that's good news.  I also checked D13 and D8.  They match the outline on the board, so they should be good.  I will try again tomorrow when I've had some rest.  Sometimes I've found fresh eyes help me see things I missed the night before.

Joseph




On Tuesday, April 29, 2014 9:15 PM, Don Wilhelm-4 [via Elecraft] <ml-node+s365791n7588159h64 at n2.nabble.com> wrote:
 
Joseph, 

See if the VFO is oscillating.  Check the internal counter probe by 
plugging it into TP2 and use menu CAL FCTR - you should see a frequency 
near 4913 kHz (the BFO frequency).  If that is good, the counter probe 
should be working.  Then plug the probe into TP1.  The frequency should 
be near the K2 dial frequency plus 4913 kHz.  If you see that frequency, 
all is OK with the VFO. 

If you instead see all zeros, the VFO is not oscillating, and you will 
have to figure out why. 
You have already checked the winding of T5, so there may be something 
else.  Check the orientation of D13 and D8 as starters. Then eliminate 
the VFO ALC from the picture by placing a short from the drsin og Q17 to 
ground (a convenient place to do that is to put a temporary solder 
bridge across the leads of C50).  Do you get a VFO frequency reading 
with that in place?  If so check the soldering of the VFO ALC 
components.  Look on the schematic and find on sheet 1 for the RF Board 
all the components in the area labeled VFO ALC and check the soldering 
of all those components - remove the solder bridge from C50 and see if 
it still oscillates.  If it does, you should be on your way to success. 

73, 
Don W3FPR 

On 4/29/2014 9:13 PM, Joseph Baxley via Elecraft wrote: 

> Don,  Matt, 
> 
> I looked at the transformer and have double checked him.  I saw that there 
> was electrical continuity between leads 1 & 2 and 3 & 4 (i.e. zero Ohm 
> resistance between said leads).  Also, 3 & 4 are the green leads.  I checked 
> that the green wires weren't crossing and that they were spaced each turn 
> between the red wires.  I did notice that they weren't exactly centered, 
> with more red turns before lead three than after lead four.  I pulled the 
> transformer out and rewound the green wires to center them and see if it 
> helped any.  No dice.  Also I checked the number of turns, 16 red and 4 
> green.  I'm intimately familiar with not having properly stripped the wires. 
> That was a problem building my K1! 
> 
> I'm fairly certain then that the transformer is not the problem.  I've been 
> checking things like the diodes that run through the VCO to make sure that I 
> have not put in one backwards.  I've also been looking for cold joints or 
> solder bridges.  Haven't found one yet. 
> 
> Thanks, 
> Joseph 
> 
> 
> 
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